Chorionic Villus Sampling


Chorionic villus sampling (CVS) is a test done on some pregnant women.

The test is done to screen your baby for genetic problems.

How the test is performed

CVS can be done through the cervix (transcervical) or through your belly (transabdominal). Miscarriage rates are slightly higher when the test is done through the cervix.

The transcervical procedure is performed by inserting a thin plastic tube through the vagina and cervix to reach the placenta. The provider uses ultrasound images to help guide the tube into the best area and then removes a small sample of chorionic villus tissue.

The transabdominal procedure is performed by inserting a needle through the abdomen and uterus and into the placenta. Ultrasound is used to help guide the needle, and a small amount of tissue is drawn into the syringe. The sample is placed in a dish and evaluated in a laboratory. Test results take about 2 weeks.

How to prepare for the test

Your health care provider will explain the procedure, its risks, and alternative procedures such as amniocentesis.

You will be asked to sign a consent form before this procedure, and you may be asked to wear a hospital gown.

The morning of the procedure, you may be asked to drink fluids and refrain from urinating. Doing so fills your bladder, which helps the doctor see where to best guide the needle.

Tell your health care provider if you are allergic to iodine or shellfish, or if you have any other allergies.

How the test will feel

The ultrasound doesn't hurt. A clear, water-based conducting gel is applied to your skin to help with the transmission of the sound waves. A hand-held probe called a transducer is then moved over the area. In addition, your health care provider may apply pressure on your abdomen to find the position of your uterus.

The cleansing solution will feel cold at first and may irritate your skin if not washed off after the procedure.

Some women say the vaginal approach feels like a Pap smear with some discomfort and a feeling of pressure. There may be a small amount of vaginal bleeding following the procedure.

An obstetrician can perform this procedure in about 5 minutes, after preparation.

Why the test is performed

Some people have a greater risk than others of passing on genetic disorders to their children. A common example is pregnant women over 35.

The test is used to identify any genetic disease in your unborn baby.

Genetic counseling is recommended prior to the procedure. This will allow you to make an unhurried, informed decision about options for prenatal diagnosis.

It can be done sooner in pregnancy than amniocentesis, usually about 10 to 12 weeks of pregnancy.

Chorionic villus sampling does not detect:

  • Neural tube defects (these involve the spinal column or brain)
  • Rh incompatibility
  • Birth defects, which are problems in the way the baby's body forms

Normal Values

A normal result means there are no signs of any genetic defects in the developing baby. However the test could miss some genetic defects.


What abnormal results mean

This test can help detect more than 200 disorders. Abnormal results may be due to a number of different genetic conditions, including:

  • Down syndrome
  • Hemoglobinopathies
  • Tay-Sachs disease

Talk to your doctor about the meaning of your specific test results.

  • How the condition or defect may be treated either during or after the pregnancy
  • Special needs your child may have after birth
  • What other options you have regarding maintaining your pregnancy

What the risks are

The risks of CVS are only slightly higher than those of an amniocentesis.

Possible complications include:

  • Bleeding
  • Infection
  • Miscarriage
  • Rh incompatibility in the mother
  • Rupture of membranes

When CVS is performed after 9 weeks gestational age, limb problems are no more frequent than in pregnancies without such testing.

Special considerations

If your blood is Rh negative, you may receive RhoGAM to prevent Rh incompatibility.

You will receive a follow-up ultrasound 2 to 4 days after the procedure to make sure the pregnancy is proceeding normally.


Simpson JL, Holzgreve W, Driscoll DA. Genetic counseling and genetic screening. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics:Normal and Problem Pregnancies. 6th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2012:chap 10.

Simpson JL, Richards DA, Otao L, Driscoll DA. Prenatal genetic diagnosis. In: Gabbe SG, Niebyl JR, Simpson JL ,eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2012:chap 11. 

Review Date: 8/7/2012

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